1. Field of the Invention
The present invention relates to a stator of an alternator driven by an internal combustion engine, for example, and in particular, relates to a stator construction for an automotive alternator mounted to an automotive vehicle such as a passenger car or a truck.
2. Description of the Related Art
FIG. 25 is a side elevation showing part of a stator of a conventional automotive alternator such as described in Japanese Patent No. 2927288, for example. FIG. 26 is a perspective showing a conductor segment used in the stator of the conventional automotive alternator shown in FIG. 25, and FIGS. 27 and 28 are perspectives from a front end and a rear end, respectively, of part of the stator of the conventional automotive alternator shown in FIG. 25.
In FIGS. 25 to 28, the stator 50 includes: a stator core 51; a stator winding 52 wound onto the stator core 51; and insulators 53 mounted inside slots 51a, the insulators 53 insulating the stator winding 52 from the stator core 51. The stator core 51 is a cylindrical laminated core laminated by stacking thin steel plates, and has a number of slots 51a extending axially disposed at even pitch circumferentially so as to be open on an inner circumferential side. In this case, ninety-six slots 51a are formed so as to house two three-phase winding portions such that the number of slots housing each phase of winding portion corresponds to the number of magnetic poles (sixteen) in a rotor (not shown). The stator winding 52 is constructed by joining a number of short conductor segments 54 in a predetermined winding pattern.
The conductor segments 54 are formed into a general U shape from an insulated copper wire material having a rectangular cross section, and are inserted two at a time from an axial rear end into pairs of slots 51a six slots apart (a pitch of one magnetic pole). Then, end portions of the conductor segments 54 extending outwards at a front end are joined to each other to constitute the stator winding 52.
More specifically, in pairs of slots 15a six slots apart, first conductor segments 54 are inserted from the rear end into first positions from an outer circumferential side within first slots 51a and into second positions from the outer circumferential side within second slots 51a, and second conductor segments 54 are inserted from the rear end into third positions from the outer circumferential side within the first slots 51a and into fourth positions from the outer circumferential side within the second slots 51a. Thus, within each slot 15a, four straight portions 54a of the conductor segments 54 are arranged to line up in a row in a radial direction.
Then, end portions 54b of the conductor segments 54 extending outwards at the front end from the first positions from the outer circumferential side within the first slots 51a and end portions 54b of the conductor segments 54 extending outwards at the front end from the second positions from the outer circumferential side within the second slots 51a six slots away in a clockwise direction from the first slots 51a are joined to form an outer layer winding having two turns. In addition, end portions 54b of the conductor segments 54 extending outwards at the front end from the third positions from the outer circumferential side within the first slots 51a and end portions 54b of the conductor segments 54 extending outwards at the front end from the fourth positions from the outer circumferential side within the second slots 51a six slots away in a clockwise direction from the first slots 51a are joined to form an inner layer winding having two turns.
In addition, the inner-layer winding and outer-layer winding constituted by the conductor segments 54 inserted into the pairs of slots 51a six slots apart are connected in series to form one winding phase portion having four turns.
A total of six winding phase portions each having four turns are formed in this manner such that the slots into which the conductor segments 54 of each winding phase portion are inserted are offset by one slot each. The stator winding 52 composed of two three-phase stator winding portions is constructed by connecting the winding phase portions three apiece into alternating-current connections.
In the conventional stator 50 constructed in this manner, at the rear end of the stator core 51, turn portions 54c of the pairs of conductor segments 54 inserted into the same pairs of slots 15a are lined up in rows in a radial direction. As a result, the turn portions 54c are arranged in two rows circumferentially to constitute a rear-end coil end group.
At the front end of the stator core 51, on the other hand, joint portions formed by joining the end portions 54b of the conductor segments 54 extending outwards at the front end from the first positions from the outer circumferential side within the first slots 51a and the end portions 54b of the conductor segments 54 extending outwards at the front end from the second positions from the outer circumferential side within the second slots 51a six slots away, and joint portions formed by joining the end portions 54b of the conductor segments 54 extending outwards at the front end from the third positions from the outer circumferential side within the first slots 51a and the end portions 54b of the conductor segments 54 extending outwards at the front end from the fourth positions from the outer circumferential side within the second slots 51a six slots away are arranged to line up radially. As a result, joint portions formed by joining end portions 54b to each other are arranged in two rows circumferentially to constitute a front-end coil end group.
In the stator 50 of the conventional automotive alternator, as explained above, the stator winding 52 is constructed by inserting short conductor segments 54 formed in the general U shape into the slots 51a of the stator core 51 from the rear end, and joining end portions 54b of the conductor segments 54 extending outwards at the front end.
Thus, because the front-end coil end group is constructed by circumferentially arranging the joint portions formed by joining the end portions 54b, which have lost their insulation due to soldering or welding, the coil-end construction is easily corroded by exposure to moisture, making corrosion resistance extremely low.
Furthermore, because the front-end coil end group is composed of two rows of ninety-six joint portions, i.e., 192 joint portions, the construction facilitates short-circuiting between the joint portions, increasing the likelihood of short-circuiting accidents.
A large number of the short conductor segments 54 must be inserted into the stator core 51 and their end portions 54b must be joined by welding, soldering, etc., significantly reducing operability. Furthermore, the amount of each conductor segment 54 which is inserted into the slots 51a must be greater than the length of the stator core 51, facilitating damage to the insulation and reducing the quality of the finished product. In addition, when joining the end portions 54b, short-circuiting often occurs between the joint portions due to spilt solder or weld melt, significantly decreasing mass-producibility.
In the conventional stator 50, the end portions 54b of the conductor segments 54 are joined to each other by clamping a portion thereof in a jig, and soldering or welding the tips thereof. Thus, because clamping area is required for the jig and expansion of the soldered portions or welded portions occurs, the height of the coil ends is increased and space between the joint portions is reduced. Furthermore, when the end portions 54b of the conductor segments 54 are welded, the conductor segments 54 are softened by temperature increases during welding, leading to decreases in the rigidity of the stator. As a result, when the conventional stator 50 is mounted to an automotive alternator, coil leakage reactance in the coil end portions is increased, causing output to deteriorate, wind resistance is increased, exacerbating wind noise, and rigidity of the stator is reduced, decreasing the effective reduction in magnetic noise.
The present invention aims to solve the above problems and an object of the present invention is to provide a stator for an alternator increasing corrosion resistance and insulation properties by significantly reducing the number of joints in the coil ends using winding assemblies composed of an arrangement of a number of winding sub-portions each having one turn composed of continuous wire, and improving assembly and productivity by improving the installation of the windings into the stator core.
In order to achieve the above object, according to one aspect of the present invention, there is provided a stator for an alternator, including:
a cylindrical stator core composed of a laminated core formed with a number of slots extending axially at a predetermined pitch in a circumferential direction; and
a polyphase stator winding including a number of winding sub-portions in each of which a long strand of wire is wound so as to alternately occupy an inner layer and an outer layer in a slot depth direction within the slots at intervals of a predetermined number of slots, the strand of wire folding back outside the slots at axial end surfaces of the stator core,
wherein the winding sub-portions are constituted by at least one winding assembly composed of a pair of first and second winding groups, the first winding group including a number of first winding sub-portions each having one turn constructed by winding one of the strands of wire so as to alternately occupy an inner layer and an outer layer in a slot depth direction within the slots at intervals of the predetermined number of slots, the first winding sub-portions being disposed at a pitch of one slot from each other and being equal in number to the predetermined number of slots, and the second winding group including a number of second winding sub-portions each having one turn constructed by winding one of the strands of wire so as to alternately occupy an inner layer and an outer layer in a slot depth direction within the slots at intervals of the predetermined number of slots and so as to be inversely wound and offset by an electrical angle of 180xc2x0 relative to the first winding sub-portions, the second winding sub-portions being disposed at a pitch of one slot from each other and being equal in number to the predetermined number of slots.